Ethernet has become the most popular physical layer for local area networks and is finding a market in larger data networks (i.e. metropolitan area and wide area). The popularity of ethernet is due in part to the good balance found between cost, speed and installation and maintenance difficulty.
The desire to reduce operating costs in networks of all sizes has produced the movement towards networks that can provide multiple services, such as carrying voice, video and data. Many of the current solutions to this problem have relied on ATM switching to map multiple services onto a network. These ATM networks typically operate at speeds between DS-1 (1.544 kbps) to OC-48 (2.5 Gbps) but the cost resulting from the higher speed complex processing leads to expensive network solutions. In addition, as traffic demands grow the evolution to faster ATM products is very costly. Further, expensive equipment is required to connect to an ATM-based network.
While ATM cells are effective for controlling “first mile jitter” problems, they are inefficient for carrying both voice and data as the cells are too long for voice but too short for data.
The use of frame-based ethernet, especially Gigabit ethernet, as a solution for the problems encountered with data traffic using ATM switching has been capitalized in the metropolitan area network (MAN) by providers such as Yipes™ and Telseon™. However, current high-speed ethernet-based networks only provide a single data service.
As the transmission rate for ethernet has increased to 1 Gbps and 10 Gbps it becomes possible to mix real-time traffic with large data frames without incurring large delays since the real-time packets no longer incur a long delay waiting for the completion of the transmission of a large data packet. For example, a 1500 byte data packet only requires 1.2 microseconds on an Ethernet network where as at ATM OC-3 rates (150 Mbps) an ATM cell requires a similar order of magnitude time at 2.8 microsceonds.
Although ATM networks operate at slower speeds than other networks, for example ethernet-based networks, ATM provides a guaranteed level of service not provided by ethernet-based networks. ATM networks offer Quality of Service (QoS) that guarantees a throughput level on the network between origination and destination.
The advantage of ATM networks is that this QoS ensures that under traffic congestion conditions some users can be guaranteed that their traffic will never be discarded. This characteristics makes ATM attractive for real-time applications, such as circuit emulation, where even small amounts of information loss can severely impact the service. Ethernet networks on the other hand are only able to assign traffic to classes that have different traffic handling characteristics. Unfortunately, these classes do not guarantee that data within these classes is never discarded. If the total volume of traffic requests for a specific class exceeds the bandwidth assigned to that class traffic will be discarded.
Further, since the path taken by packets in an ethernet network is not known by the source and there is no switch by switch allocation of bandwidth on trunks, an ethernet network is not able to allocate bandwidth to specific data flows.